TC

AGa

b

a

ARRA

KCSS

1

pimsta

sttulFltaPm(

0d

Journal of Geodynamics 49 (2010) 287–295

Contents lists available at ScienceDirect

Journal of Geodynamics

journa l homepage: ht tp : / /www.e lsev ier .com/ locate / jog

he Loncopué Trough: A Cenozoic basin produced by extension in the southernentral Andes

ndrés Folgueraa,∗, Emilio Rojas Veraa, Germán Bottesib,onzalo Zamora Valcarceb, Victor A. Ramosa

Laboratorio de Tectónica Andina, Universidad de Buenos Aires, CONICET, ArgentinaYPF, Dirección de Exploración y Desarrollo de Negocios, Argentina

r t i c l e i n f o

rticle history:eceived 4 August 2009eceived in revised form 13 January 2010ccepted 13 January 2010

a b s t r a c t

The Loncopué Trough is located in the hinterland Andean zone between 36◦30′ and 39◦S. It constitutes atopographic low bounded by normal faults and filled by lavas and sediments less than 5 Ma old. Repro-cessed seismic lines show wedge-like depocenters up to 1700 m deep associated with high-angle faults,correlated with the 27–17 Ma Cura Mallín basin deposits, and buried beneath Pliocene to Quaternary

eywords:enozoic extensionynextensional sedimentationouthern Central Andes

successions and Late Miocene foreland sequences. The southern Central Andes seem to have been underextension in the hinterland zone some 27 Ma ago and again at approximately 5 Ma ago. This last exten-sional period could have been the product of slab steepening after a shallow subduction cycle in thearea, although other alternatives are discussed. Orogenic wedge topography, altered by the first exten-sional stage in the area, was recovered through Late Miocene inversion, and was associated with forelandsequences. However, since the last extension (<5 Ma) the Andes have not recovered their characteristic

at co

contractional behavior th

. Introduction

The Andean retroarc zone between 35◦ and 40◦S (Fig. 1), andarticularly between 36◦30′ and 39◦S where the Loncopué Trough

s developed, constitutes an outstanding site to address non-steadyountain building since the Andean phase of deformation started

ome 100 Ma ago. Here we present field and geophysical data fromhat specific site to exemplify extensional reactivation of the foldnd thrust belt that have produced substantial topographic losses.

The southern Central Andes (28–40◦S) can be divided in twoectors based on their evolution during the last 17 Ma. Since thatime, the northern region between 28◦ and 33◦S has experiencedhe Pampean flat subduction associated with basement forelandplifts. It is limited eastward by a neotectonic compressional front

ocated some 750 km from the trench (Fig. 1) (Costa and Vita-inzi, 1996; Ramos et al., 2002). Seismic tomographies at thoseatitudes show fast P wave-velocities implying a cold setting abovehe horizontal subducted slab (Gilbert et al., 2006). Contrastingly,

southern segment between 35◦ and 40◦S has abandoned theayenia shallow subduction zone since 5 Ma, as evidenced byigration of the volcanic arc more than 500 km toward the foreland

Fig. 2A) (Kay et al., 2006a). Seismic tomography at approximately

∗ Corresponding author.E-mail address: andresfolguera2@yahoo.com.ar (A. Folguera).

264-3707/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.oi:10.1016/j.jog.2010.01.009

ntrolled past orogenic growth.© 2010 Elsevier Ltd. All rights reserved.

35.5–36◦S (Wagner et al., 2005; Gilbert et al., 2006) and receiverfunction profiles at 39◦S (Yuan et al., 2006) (Fig. 1) show (i) largesubcrustal low-velocity arrivals interpreted as mantle melts and/orvolatiles and (ii) an attenuated lower crust. This scenario has beeninterpreted as derived from asthenosphere injection in a broad-ened asthenospheric wedge more than 400 km away from thetrench in the retroarc area, triggering extensional deformation atthe upper crust (Fig. 2B) (Folguera et al., 2007, 2008). A 2D prelimi-nary electrical resistivity model at 36.5◦S (Burd et al., 2008) showsan “uprising highly conductive plume” with geometry compati-ble with the asthenospheric anomaly modeled from gravity data(Folguera et al., 2007). The inferred extensional deformation in thissegment would have expanded to the east, defining a Quaternarydeformational front (Figs. 1 and 2B) where previous compressionalstructures would be partly collapsing diachronically since ∼5 Ma(Folguera et al., 2006a). This scenario has been discussed and evencontradicted by other studies, the main discrepancies based onlyon surficial data (Lavenu and Cembrano, 1999; Backé et al., 2006;Melnick et al., 2006a,b; Rosenau et al., 2006; Galland et al., 2007).

This work, through interpretation of reprocessed seismic linesand field work, proposes a crustal-scale extensional nature of one of

the main less than 5 Ma depocenters in the southern Central Andes,as well as its polyphasic nature, indicating repeated instability ofthe orogenic wedge through time. Finally, its origin is discussed inlight of current tectonic models discussed for this Andean segmentduring the Neogene.

288 A. Folguera et al. / Journal of Geodynamics 49 (2010) 287–295

Fig. 1. Southern Central and Northern Patagonian Andes and location of the present Pampean flat subduction zone and the Late Miocene Payenia shallow subduction zoneto the south, proposed by Kay et al. (2006a). The neotectonic front is also indicated as well as its variable mechanics. The two dashed lines indicate transects along whichabnormally heated mantle and crustal attenuation processes have been identified.

Fig. 2. (A) Late Miocene tectonic setting for the area between 33◦ and 41◦S, with locations of easternmost arc-related rocks (after Kay et al., 2006a), synorogenic depocenters,and contractional structures developed at that time (Ramos and Folguera, 2005). (B) Extensional deformation developed after 5 Ma in the same area controlling emplacementof intraplate series and location of the Loncopué Trough and the adjacent Agrio fold and thrust belt.

A. Folguera et al. / Journal of Geodynamics 49 (2010) 287–295 289

F ain exfi he twc pectiv

2

bs2aEaVclb2sdec1MaedhTgi

ig. 3. The Loncopué Trough flanking the Main Andes between 36◦ and 39◦S and meld in the arc-western retroarc region (contours taken from Folguera et al., 2007). Torresponding to the northern and southern axial parts of the Loncopué Trough res

. Retroarc geological setting

The eastern slope of the Andes between 36◦ and 39◦S is formedy the main Andes, the product of Late Miocene tectonic inver-ion of the 27–17 Ma Cura Mallín basin (Jordan et al., 2001; Burns,002; Radic et al., 2002; Melnick et al., 2006a,b) and the Agrio foldnd thrust belt to the east (Fig. 3). The latter constitutes a Latearly Cretaceous to Eocene fold and thrust belt mildly reactivatedt the time of basin inversion in the west (Groeber, 1929; Zamoraalcarce et al., 2008) (Fig. 2). The Late Early Cretaceous to Eoceneontractional deformational stage and consequent uplift at theseatitudes is determined from (i) fission track data yielding an ageetween 70 and 50 Ma (Kay et al., 2006b; Zamora Valcarce et al.,008), (ii) zircon detrital provenance data from the hinterland inynorogenic depocenters dated at <97 Ma (Ramos et al., 2008), (iii)ating of postdeformational intrusives (<105 Ma) (Zamora Valcarcet al., 2006), and (iv) a regional unconformity between Latest Creta-eous to Paleocene sequences and Early Cretaceous strata (Groeber,929; Llambías and Rapela, 1989; Franchini et al., 2003). The Curaallín basin is interpreted as formed by a series of synextensional

nd diachronous depocenters (Burns, 2002; Radic et al., 2002; Utgét al., 2009), inverted since 17–18 Ma as determined by fission track

ata (Spikings et al., 2008) and field studies (Utgé et al., 2009). Theseave been unconformably overlain by the Mid to Late Miocenerapa–Trapa and Mitrauquén Formations, interpreted as synoro-enic deposits (Melnick et al., 2006a,b). Both the Cura Mallín basinnversion and late reactivation of the Agrio fold and thrust belt

tensional structures. Numbers are in mGal and correspond to the residual gravityo seismic lines interpreted in the present work are indicated with dashed segmentsely.

in Late Miocene times have been related to a shallow subductionregime (Payenia shallow subduction zone), as evidenced by con-temporaneous eastward arc expansion (Kay et al., 2006a,b).

3. Early Pliocene to Quaternary extensional deformation inthe Loncopué Trough

The Loncopué Trough is on the eastern flank of the highest Andes(Main Andes) between 36◦30′and 39◦S (Fig. 3), although its maxi-mum topographic expression lies between 38◦ and 39◦S. The axialpart of the trough is marked by a series of low residual gravityanomalies in contradistinction to the Agrio fold and thrust beltto the east and the main Andes to the west, where higher valuesof residual gravity are reached (Fig. 3). Moreover, the entire areaoccupied by the Loncopué Trough and the Agrio fold and thrustbelt is characterized by strong isostatic anomalies coincident withthe area of crustal attenuation (Yuan et al., 2006), indicating that itcould be subcompensated.

On the basis of morphological observations, Munoz and Stern(1985) suggested that the axially depressed sector of the LoncopuéTrough is bounded by two N–S fault systems, controlling EarlyPliocene to Quaternary monogenetic alkaline basaltic eruptions.

Basal Loncopué Trough sequences that were dated in the north-ern part of the trough at 4 ± 0.5 Ma, culminate in a lava plateau of1.7 ± 0.2 Ma sparsely covered by 1.4 ± 0.4–1.2 ± 0.1 monogeneticeruptions (Folguera et al., 2004). In the southern and middlesections of the trough, similar basal ages up to 5–6 Ma were

290 A. Folguera et al. / Journal of Geodynamics 49 (2010) 287–295

F ss tha

rA0t1v

Fei

ig. 4. Western Loncopué Trough system at 38◦S where a series of halfgrabens of le

eported for the plateau sequences (Linares and González, 1990).t about 39◦S, monogenetic centers range between 2.30 ± 0.3 and

.47 ± 0.2 Ma (Linares and González, 1990) on the axial part of therough, while on its western boundary they have been dated from.6 ± 0.2 to 0.9 ± 0.3 Ma (Munoz and Stern, 1985, 1988). Youngestolcanic activity is concentrated at around 38◦S in the axial

ig. 5. Neotectonic deformation in the western Agrio fold and thrust belt. This occurredvent is not related to stacking of thrust sheets east of the fold and thrust belt, which wouts main features. (B) Detail of the area of neotectonic deformation. (C) Structural profile

n 100 m across affect Late Pliocene to Quaternary lava flows (see location in Fig. 3).

trough, where basaltic flows interfinger with postglacial lacustrinedeposits (Groeber, 1928). A poorly evolved alkaline magmatism,

together with low 87Sr/86Sr initial ratios near 0.7040, relates thisvolcanic field to an extensional regime (Munoz Bravo et al., 1989).

The youngest tectonic activity in the Loncopué Trough is datedby scarps affecting lava flows at the central part of the trough

previous to 105 Ma, the age of postdeformational dykes (A). This rapid and youngld require another uplift mechanism. (A) DEM of the Agrio fold and thrust belt and

(see location in (A)).

A. Folguera et al. / Journal of Geodynamics 49 (2010) 287–295 291

F esternv Formav estern

iatoA

dagftcTevsm(ap

a

ig. 6. Eastern Loncopué Trough system at 38◦S, where normal faults affect the wolcanics. (B) Normal fault juxtaposing late Early Jurassic sandstones of the La Lajaolcanics are displaced. (C) Perspective view of an Aster draped over a DEM in the w

nterfingered with postglacial lacustrine sediments (Rojas Vera etl., 2008, 2009). Maximum depocenters belonging to this Plioceneo Quaternary stage are 1500–1900 m thick, with an average valuef 1000 m, exposed by exceptional glacial activity in the mainndes.

The two Loncopué fault boundaries and their nature (Fig. 3) wereetermined by field observations, where Quaternary sequencesre extensionally displaced (Figs. 4 and 5), exhibiting linear topo-raphic breaks tens to more than one hundred kilometres long,acing the axial low. The western boundary fault zone is formed athe surface by a series of halfgrabens less than 100 m across, asso-iated with east-facing scarps affecting Quaternary lavas (Fig. 4).he eastern boundary fault zone represents a series of west- andast-facing normal fault scarps affecting Quaternary lavas and pre-iously deformed Mesozoic strata (Figs. 5 and 6). The Mesozoictrata were folded previously at 105 Ma, the age of postdefor-ational dykes intruded into the compressional structure (Fig. 6)

Zamora Valcarce et al., 2006). Therefore, extensional deformationffecting Quaternary rocks is not likely related to the contractionalhenomena.

Even though extension is (i) registered at both trough bound-ries, leaving a symmetrical trough in between, (ii) affecting

part of the Agrio fold and thrust belt. (A) Extensional scarps affecting Quaternarytion on top of Early Jurassic shales of the Los Molles Formation, where QuaternaryAgrio fold and thrust belt and adjacent Loncopué Trough. (D) Interpretation of (C).

Pliocene to Quaternary rocks, and (iii) temporally unconnectedwith contractional phases determined at these orogenic sections,its identified short wavelength allows alternative explanations.These structures could be associated with superficial extensionof deeper contractional structures active in the Andean foothills.However, our interpretation is that their length, for individual seg-ments of the order of 20 km and for fault systems around 40–60 km,corresponds to rather deeply rooted structures.

4. Late Oligocene to Early Miocene extensionaldeformation in the Loncopué Trough

Strata of 27–17 Ma age in the Cura Mallín basin are uncon-formably overlain by Early Pliocene sequences in the main Andesbetween 36◦ and 39◦S (Fig. 3) (Suárez and Emparán, 1995; Jordanet al., 2001; Burns, 2002), and in the axial part of the LoncopuéTrough north of 37◦30′S (Fig. 3). Late Oligocene to Early Miocene

strata are systematically exposed on the western side of the Andesbetween 38◦ and 39◦S (Fig. 3) and on both sides of the Andes northof 38◦S (Folguera et al., 2006b; Melnick et al., 2006a,b). The mechan-ics of subsidence has been discussed extensively in the last decade,revealing two opposing points of view. On the one hand, Cobbold et

292 A. Folguera et al. / Journal of Geodynamics 49 (2010) 287–295

Fig. 7. 2D W–E oriented seismic line across the axial part of the southern Loncopué Trough at 38◦S, where a wedge-like depocenter thickens towards the eastern main faultboundary and is characterized internally by minor extensional structures; registered times for the deepest reflectors would imply a maximum infill of the order of 1400 m,considering an interval velocity derived from stacking velocities of 2800 m/s. See location with respect to the axial Loncopué Trough in Fig. 3. Ages of units rely on correlationsand are not determined directly. (A) Seismic line. (B) Interpretation of (A) superimposed on it. (C) Complete interpretation.

Fig. 8. (A) 2D W–E oriented seismic line across the axial part of the northern Loncopué Trough at 37◦S, where a series of wedge-like depocenters thickens to the west;registered times for the deepest reflectors would imply a maximum infill of the order of 1100 m, considering an interval velocity derived from stacking velocities of 2800 m/s.See location with respect to the axial Loncopué Trough in Fig. 3. (B) Interpretation of (A). Ages of units rely on correlations and are not determined directly.

Geody

alCSedeststabnecwfstalswaFl(a

FaB

A. Folguera et al. / Journal of

l. (2008) suggested that those sequences constitute a typical fore-and basin associated with the steady uplift of the Andes from Lateretaceous to Neogene times. On the contrary Spalletti and Dallaalda (1996), Suárez and Emparán (1995), Jordan et al. (2001), Radict al. (2002) and Burns (2002), among others, suggest that thoseepocenters were part of an intra-arc extensional basin. Most of thevidence favoring each hypothesis was based on sedimentologicaltudies, regional basin studies, supposed progressive unconformi-ies, and analyses of low quality 2D seismic lines. Figs. 7 and 8how reprocessed seismic lines where wedge-shaped depocen-ers 1100–1400 m thick with variable polarity and dimensionsre recognized. Particularly in Fig. 7, halfgrabens are controlledy west-dipping high-angle faults. These are characterized inter-ally by a series of narrower wedges which truncate each other byrosional surfaces (referred as synrift 1–4). These wedges are asso-iated above with anticlines suggesting that related normal faultsere partly inverted (Fig. 7) before Pliocene times (the oldest non-

olded rocks in the area). Onlapping reflectors on top of the invertedynrift wedges support the idea that synorogenic sedimentationook place at the time of inversion in the Loncopué Trough, presum-bly in late Miocene times. This series of halfgraben depocenters isocated across the axial part of the southern Loncopué Trough, andeems to be associated with a west-dipping main fault boundary,here strata reach their maximum thickness. This is coincident

t the surface with the eastern fault boundary zone indicated inigs. 3 and 5. Synrift packages are correlated with the Cura Mal-ín strata outcropping immediately to the west in the main AndesFig. 3), while onlapping sequences are assigned to the Trapa–Trapand Mitrauquén Formations following the same criteria.

ig. 9. Structural cross section along the eastern slope of the Andes at 38◦S, where Cenozffect the western section of a mainly Late Cretaceous fold and thrust belt (modified fromohm et al. (2002), and isostatic anomalies from Folguera et al. (2007).

namics 49 (2010) 287–295 293

The seismic line in Fig. 8 is interpreted as a series of halfgrabenscontrolled by east-dipping normal faults. These seem to be mildlyinverted judging by the presence of broad anticlines developedon top of the thickest sedimentary columns. Contrastingly, in theseismic line in Fig. 7, no onlapping unit is distinguishable. This isexplained by a deeper level of erosion, where Late Oligocene toEarly Miocene units are exposed at the surface (Fig. 3). This con-trasts with interpretations published by Jordan et al. (2001) fromthe same original data, where they infer a western master fault con-trolling the depocenter. This different interpretation is attributableto the quality of information. While Jordan et al. (2001) dealt withoriginally processed seismic data, we have used recently repro-cessed data that reveal features hidden in previous lines.

5. Discussion and conclusions

Extensional depocenters of 27–17 and 5–0 Ma age inferredfrom seismic information and confirmed by field studies, separatedby foreland sequences, could be superimposed in the LoncopuéTrough, having produced locally the sinking of the westernmostsection of the Late Cretaceous to Eocene fold and thrust belt.Therefore, a long controversy regarding the mechanics of subsi-dence in the Loncopué trough could be saved: these foothills haveacted alternatively as a foredeep and a retroarc basin. To the east,

remnants of these Cenozoic extensional collapses constitute theAgrio fold and thrust belt (Fig. 9), emerged mainly in Late Cre-taceous to Eocene times as revealed by dating based on fissiontrack and synorogenic sedimentation. A broad isostatic anomaly(with a maximum of 40 mGal) (Fig. 9) coincides at the surface

oic halfgrabens of Late Oligocene-Early Miocene to Early Pliocene-Quaternary ageZapata et al., 1999 and Zapata and Folguera, 2005). Crustal earthquakes taken from

2 Geody

wsaHtsAdhwihatLh(toaBAtPdsttCs

A

asD

R

B

B

B

B

C

C

F

F

F

F

94 A. Folguera et al. / Journal of

ith the Loncopué Trough. At a broader scale the isostatic anomalyhows two peaks that define an amplitude compatible with therea of crustal attenuation described by Yuan et al. (2006) (Fig. 9).ypothetically, this scenario would point to the permanence of

he youngest proposed extensional phenomena that would havetarted some 5 Ma ago. Orogenic uplift in the southern Centralndes could have been interrupted at least two times through theevelopment of normal faults associated with sedimentation in theinterland zone. Subsequent periods of contractional deformationould only have incorporated Paleogene extensional depocenters

nto the orogenic wedge, while a less than 5 Ma extension would notave been inverted yet in the area. Non-steady mountain growthnd extensional deformation could be common processes duringhe evolution of the southern Central Andes at the latitudes of theoncopué Trough. Finally, as stated before, different hypothesesave been proposed to explain Quaternary extension in the area:i) as associated with local and surficial minor extension relatedo deeper compressional structures; (ii) as generated in strike-slipr low-partitioned strain settings, coexisting with compressionalnd/or transpressional structures (Lavenu and Cembrano, 1999;acké et al., 2006; Rosenau et al., 2006); and (iii) as related tondean-scale axial synorogenic collapse, coexisting with contrac-

ional behavior in the foothills (Melnick et al., 2006a,b). The Earlyliocene to Quaternary extensional stage could also be the imme-iate reaction (slab steepening) to the 18–6 Ma Payenia shallowubduction zone that affected the area. This hypothesis is based onhe fact that the area of extension less than 5 Ma old coincides withhe area of eastward expansion of the arc in Late Miocene times.auses of Late Oligocene to Early Miocene extension in the area aretill being debated.

cknowledgments

We acknowledge Randell Stephenson, Editor-in-Chief, andnonymous reviewers; and YPF SA for providing and processingeismic information. Early discussions with S.M. Kay, D. Melnick,. Dhont, and P. Cobbold are also acknowledged.

eferences

acké, G., Hervouët, Y., Dhont, D., 2006. Cenozoic extension vs. compression inthe Central Neuquen basin (S37◦–S36◦ , Argentina). In: Backbones of America-Asociación Geológica Argentina and Geological Society of America, Serie D(9),Proceedings, Mendoza, pp. 111–112.

ohm, M., Lüth, S., Echtler, H., Asch, G., Bataille, K., Bruhn, C., Rietbrock, A., Wigger,P., 2002. The Southern Andes between 36◦ and 40◦S latitude: seismicity andaverage seismic velocities. Tectonophysics 356, 275–289.

urd, A., Booker, J., Pomposiello, M., Favetto, A., Larsen, J., Giordanengo, G., OrozcoBerna, L., 2008. Electrical conductivity beneath the Payún Matrú Volcanic Field inthe Andean back-arc of Argentina near 36.5◦S: insights into the magma source.In: International Symposium on Andean Geodynamics, vol. 7, Nice, pp. 90–93.

urns, W.M., 2002. Tectonics of the Southern Andes from stratigraphic, ther-mochronologic, and geochemical perspectives. PhD Thesis, Cornell University,Ithaca, NY, p. 204.

obbold, P., Rossello, E., Marques, F., 2008. Where is the evidence for Oligocenerifting in the Andes? Is it in the Loncopué Basin of Argentina? In: InternationalSymposium on Andean Geodynamics, vol. 7, Nize, pp. 148–151.

osta, C., Vita-Finzi, C., 1996. Late Holocene faulting in the southeast Sierras Pam-peanas of Argentina. Geology 24 (12), 1127–1130.

olguera, A., Ramos, V.A., Hermanns, R.L., Naranjo, J., 2004. Neotectonics inthe foothills of the southernmost central Andes (37◦–38◦S): evidence ofstrike-slip displacement along the Antinir-Copahue fault zone. Tectonics 23,doi:10.1029/2003TC001533 (TC5008).

olguera, A., Zapata, T., Ramos, V.A., 2006a. Late Cenozoic Extension and the evo-lution of the Neuquén Andes. In: Kay, S.M., Ramos, V.A. (Eds.), Evolution of anAndean Margin: A Tectonic and Magmatic View from the Andes to the NeuquénBasin (35–39◦S), pp. 267–285, Spec. Pap. Geol. Soc. America 407.

olguera, A., Ramos, V., González Díaz, E., Hermanns, R., 2006b. Miocene to Quater-

nary deformation of the Guanacos fold and thrust belt in the Neuquén Andesbetween 37◦ and 37◦30′S. In: Kay, S.M., Ramos, V.A. (Eds.), Evolution of anAndean Margin: A Tectonic and Magmatic View from the Andes to the NeuquénBasin (35–39◦S), pp. 247–266, Spec. Pap. Geol. Soc. America 407.

olguera, A., Introcaso, A., Giménez, M., Ruiz, F., Martínez, P., Tunstall, C., GarcíaMorabito, E., Ramos, V.A., 2007. Crustal attenuation in the Southern Andean

namics 49 (2010) 287–295

retroarc determined from gravimetric studies (38◦–39◦30′S): the Lonco-Luánastenospheric anomaly. Tectonophysics, doi:10.1016/j.tecto.2007.04.001.

Folguera, A., Bottesi, G., Ramos, V., Zapata, T., 2008. Crustal collapse at theretroarc zone (2-0 Ma): Tromen volcanic plateau, Southern Central Andes(36◦40′–37◦30′S). In: Sempere, T., Folguera, A., Gerbault, M. (Eds.), NewInsights into Andean Evolution: An Introduction to Contributions from the6th ISAG Symposium, Barcelona, 2005. Tectonophysics, doi:10.1016/j.tecto.2007.12.013.

Franchini, M.B., López Escobar, L., Shalamuk, I.B.A., Meinert, L.D., 2003. Paleocene,calc-alkaline subvolcanic rocks from Nevazón Hill area (NW Chos Malal FoldBelt), Neuquén, Argentina, and comparison with granitoids of the Neuquén-Mendoza volcanic province. Journal of South American Earth Sciences 16,399–421.

Galland, O., Hallot, E., Cobbold, R., Ruffet, G., Brémond d’Ars, J., 2007. Volcan-ism in a compressional Andean setting: a structural and geochronologicalstudy of Tromen volcano (Neuquén province, Argentina). Tectonics, 26,doi:10.1029/2006TC002011 (TC4010).

Gilbert, H., Beck, S., Zandt, G., 2006. Lithospheric and upper mantle structure ofcentral Chile and Argentina. Geophysical Journal Internacional 165 (1), 383,doi:10.1111/j.1365-246X.2006.02867.x.

Groeber, P., 1928. Traslado del vulcanismo de la falda oriental de la cordillera haciala ladera occidental. Anales de la Sociedad Argentina de Estudios Geográficos(GAEA) 3 (1), 210–218, Buenos Aires.

Groeber, P., 1929. Líneas fundamentales de la geología del Neuquén, sur de Men-dozay regiones adyacentes, Pub. Dirección de Geologíay Minería58, 110 pp.

Jordan, T.E., Burns, W.M., Veiga, R., Pángaro, F., Copeland, P., Kelley, S., Mpodozis,C., 2001. Extension and basin formation in the southern Andes caused byincreased convergence rate: a mid-Cenozoic trigger for the Andes. Tectonics 20,308–324.

Kay, S.M., Mancilla, O., Copeland, P., 2006a. Evolution of the Backarc Chachahuénvolcanic complex at 37◦S latitude over a transient Miocene shallow subductionzone under the Neuquén Basin. In: Kay, S.M., Ramos, V.A. (Eds.), Evolution of anAndean Margin: A Tectonic and Magmatic View from the Andes to the NeuquénBasin (35–39◦S), pp. 215–246, Spec. Pap. Geol. Soc. America 407.

Kay, S.M., Burns, M., Copeland, P., 2006b. Upper Cretaceous to Holocene Magmatismover the Neuquén basin: evidence for transient shallowing of the subductionzone under the Neuquén Andes (36◦S to 38◦S latitude). In: Kay, S.M., Ramos, V.A.(Eds.), Evolution of an Andean Margin: A Tectonic and Magmatic View from theAndes to the Neuquén Basin (35–39◦S), pp. 19–60, Spec. Pap. Geol. Soc. America407.

Lavenu, A., Cembrano, J., 1999. Compressional and tranpressional stress patternfor Pliocene and Quaternary brittle deformation in fore arc and intra arczones (Andes of Central and Southern Chile). Journal of Structural Geology 21,1669–1691.

Linares, E., González, R., 1990. Catálogo de edades radimétricas de la RepúblicaArgentina 1957–1987. Asociación Geológica Argentina, Pub. Esp. Serie B, Didác-ticay Complementaria 19, 628 pp.

Llambías, E.J., Rapela, C.W., 1989. Las vulcanitas de Colipilli, Neuquén (37◦S) y surelación con otras unidades paleógenas de la cordillera. Revista de la AsociaciónGeológica Argentina 44 (1–4), 224–236.

Melnick, D., Rosenau, M., Folguera, A., Echtler, H., 2006a. Neogene Tectonics of theWestern flank of the Neuquén Andes, 37◦–39◦30′S. In: Kay, S.M., Ramos, V.A.(Eds.), Evolution of an Andean Margin: A Tectonic and Magmatic View from theAndes to the Neuquén Basin (35–39◦S). Spec. Pap. Geol. Soc. America, 407, pp.73–95.

Melnick, D., Charlet, F., Echtler, H., De Batist, M., 2006b. Incipient axial collapse ofthe Main Cordillera and strain partitioning gradient between the central andPatagonian Andes, Lago Laja, Chile. Tectonics 25, doi:10.1029/2005TC001918(TC5004), 22 pp.

Munoz, J., Stern, C., 1985. El complejo volcánico Pino Hachado en el sec-tor nor-occidental de la Patagonia (388-398S): volcanismo plio-cuaternariotrasarco en Sudamérica. IV Congreso Geológico Chileno (Antofagasta). Actas 3,381–412.

Munoz, J., Stern, C., 1988. The Quaternary volcanic belt of the Southern continentalmargin of South America: transverse structural and petrochemical variationsacross the segment between 38◦S and 39◦S. Journal of South American EarthSciences 1, 147–162.

Munoz Bravo, J., Stern, C., Bermúdez, A., Delpino, D., Dobbs, M.F., Frey, F.A., 1989. Elvolcanismo plio-cuaternario a través de los 38◦ y 39◦S de los Andes. Revista dela Asociación Geológica Argentina 44, 270–286.

Ramos, V.A., Cristallini, E., Pérez, D.J., 2002. The Pampean flat-slab of the CentralAndes. Journal of South American Earth Sciences 15, 59–78.

Ramos, V.A., Folguera, A., 2005. Tectonic evolution of the Andes of Neuquén: con-straints derived from the magmatic arc and foreland deformation. In: Veiga,G.D., Spalletti, L., Howell, J.A., Schwarz, E. (Eds.), The Neuquén Basin: A CaseStudy in Sequence Stratigraphy and Basin Dynamics. Special Publications, vol.252. Geological Society, London, pp. 15–35.

Ramos, V.A., Pimentel, M., Tunik, M., 2008. Late Cretaceous synorogenic depositsof the Neuquén Basin (36–39◦S): age constraints from U-Pb dating in detritalzircons. In: International Symposium on Andean Geodynamics, vol. 7, Nize, pp.

423–426.

Radic, J., Rojas, L., Carpinelli, A., Zurita, E., 2002. Evolución tectónica de la CuencaTerciaria de Cura Mallín, región cordillerana chileno-argentina (36◦30′–39◦S).In: Congreso Geológico Argentino, vol. 15, El Calafate, pp. 233–241.

Rojas Vera, E., Folguera, A., Zamora Valcarce, G., Ramos, V.A., 2008. The LoncopuéTrough: a major orogenic collapse at the western Agrio fold and thrust belt

Geody

R

R

S

S

S

U

A. Folguera et al. / Journal of

(Andes of Neuquén, 36◦40′–38◦40′S). In: International Symposium on AndeanGeodynamics, vol. 7, Nice, pp. 461–464.

ojas Vera, E., Folguera, A., Gímenez, M., Martínez, P., Ruiz, F., Ramos, V.A., 2009.Evolución tectónica de la fosa de Loncopué: Estructura del depocentro cuater-nario del Huecú y su relación con la sedimentación y el volcanismo. Revista dela Asociación Geológica Argentina 64 (2), 213–229.

osenau, M., Melnick, D., Echtler, H., 2006. Kinematic constraints on intra-arc shearand strain partitioning in the southern Andes between 38◦S and 42◦S latitude.Tectonics 25, doi:10.1029/2005TC001943 (TC4013), 16 pp.

palletti, L.A., Dalla Salda, L., 1996. A pull apart volcanic related Tertiary basin, anexample from the Patagonian Andes. Journal of South American Earth Sciences9 (3–4), 196–206.

pikings, R., Dungan, M., Foeken, J., Carter, A., Page, L., Stuart, F., 2008. Tec-tonic response of the central Chilean margin (35–38◦S) to the collision andsubduction of heterogeneous oceanic crust: a thermochronological study.Journal of the Geological Society 165, 941–953, doi:10.1144/0016-76492007-115.

uárez, M., Emparán, C., 1995. The stratigraphy, geochronology and paleophysiog-raphy of a Miocene fresh-water interarc basin, southern Chile. Journal of SouthAmerican Earth Sciences 8 (1), 17–31.

tgé, S., Folguera, A., Litvak, V., Ramos, V.A., 2009. Geología del sector norte de lacuenca de Cura Mallín en las Lagunas de Epulafquen, Neuquén. Revista de laAsociación Geológica Argentina 63 (2), 230–247.

namics 49 (2010) 287–295 295

Wagner, L., Beck, S., Zandt, G., 2005. Upper mantle structure in the south cen-tral Chilean subduction zone (30◦ to 36◦S). Journal of Geophysical Research,doi:10.1029/2004JB003238.

Yuan, X., Asch, G., Bataile, K., Bohm, M., Echtler, H., Kind, R., Onchen, O., Wölbern,I., 2006. Deep seismic images of the Southern Andes. In: Kay, S.M., Ramos, V.A.(Eds.), Evolution of an Andean Margin: A Tectonic and Magmatic View from theAndes to the Neuquén Basin (35–39◦S), pp. 61–72, Spec. Pap. Geol. Soc. America407.

Zamora Valcarce, G., Zapata, T., del Pino, D., Ansa, A., 2006. Structural evolution ofthe Agrio fold and thrust belt. In: Kay, S.M., Ramos, V.A. (Eds.), Evolution of anAndean Margin: A Tectonic and Magmatic View from the Andes to the NeuquénBasin (35–39◦S), pp. 125–145, Spec. Pap. Geol. Soc. America 407.

Zamora Valcarce, G., Zapata, T., Ramos, V.A., Rodriguez Monreal, F., 2008. Evolucióntectónica del frente andino de Neuquén. In: Faja Plegada del Agrio. CongresoGeológico Argentino, vol. 17, Jujuy, pp. 171–172.

Zapata, T., Folguera, A., 2005. Tectonic evolution of the Andean fold and thrustbelt of the Southern Neuquén basin, Argentina. In: Veiga, G., Spalletti, L.,

Howell, J., Schwarz, E. (Eds.), The Neuquén Basin: A Case Study in SequenceStratigraphy and Basin Dynamics, pp. 37–56, Spec. Pub. Geological Society ofLondon 252.

Zapata, T., Brissón, I., Dzelalija, F., 1999. The role of basement in the Andean foldand thrust belt of the Neuquén Basin. In: Proceedings Thrust Tectonics, London,England, pp. 122–124.